The instant disclosure relates generally to the removal and control of orbital debris. In particular, the instant disclosure relates to apparatus and methods for removing orbital debris from low Earth orbits (“LEOs”).
Objects that are in orbit around Earth as the result of space initiatives that no longer serve any function are called “orbital debris” (the term “debris” is used herein as a shorthand to refer to orbital debris). Examples of orbital debris include expired spacecraft, upper stages of launch vehicles, debris released during spacecraft separation from its launch vehicle or during mission operations, debris created as a result of spacecraft or upper stage explosions or collisions, solid rocket motor effluents, paint flecks, and thermal blankets.
Most orbital debris is concentrated in what is considered low Earth orbit (“LEO”). Indeed, orbital debris has been accumulating in LEOs between 600 km and 1200 km altitude for the past 59 years. The United States Space Surveillance Network, operated by the United States Air Force, estimates that there are more than 500,000 pieces of debris larger than 1 cm orbiting Earth today, including over 22,000 pieces larger than 10 cm that are actively tracked. This ignores millions of smaller, untrackable pieces of orbital debris. Thus, the debris density in these LEOs has reached a level of serious concern to active satellite operators.
In LEOs, the average closing speed at which collisions with orbital debris takes place is about 10 km/sec. Even though debris represents a growing international crisis, space agencies have taken almost no action to remove debris and have only limited debris sensing and tracking capabilities for objects larger than 10 cm.
Trajectory projections, based on collected data, are supplied to satellite owners and operators. Those few operators that have maneuverable satellites may try to carry out collision-avoidance maneuvers based on projections derived from debris tracking data. Such maneuvers are rarely tried, however, because the reaction times are short and the accuracy of collision predictions is often insufficient to warrant an expensive and complicated change in a satellite's orbit. Since no debris-removal flight programs have been funded, satellite operators with assets in high-density debris zones have no assurance of safety from collisions.
Although collisions can be difficult to detect, over the past several years there have been numerous reports of small debris encounters and one reported collision between an operational satellite and an expired satellite (i.e., the 2009 Iridium-Kosmos incident). Nevertheless, the frequency of collisions is trending upward, especially in the 600 km to 1200 km altitude region of near-Earth space. In addition to the already several hundred active satellites, several thousand more are planned for launch into this zone in the next few years.
While the addition of debris shielding on operating satellites may be partially effective, the collision frequency and level of damage will become progressively less tolerable over time. The prevention of future debris creation has been suggested, but the debris density has already passed the point where its increase due to ongoing collisions is unstable. Some amount of ongoing debris removal is necessary in order to maintain at least a minimum acceptable level of safety in orbit. A solution to this growing threat of catastrophic destruction of all satellite assets in the high-density debris zone has become an international mandate.
U.S. Pat. No. 4,991,799 describes an orbital debris sweeper for removing particles from orbit. This apparatus includes a central sweeper core which carries a debris monitoring unit and a plurality of large area impact panels that rotate about a central sweeper axis. In response to information from the debris monitoring unit, a computer determines whether individual monitored particles have impacted one of the rotating panels.
U.S. Pat. No. 3,277,724 is directed to a device for measuring the mass and velocity of meteoroid particles which collide therewith. The device consists of two inflatable spherical structures, one of which is concentrically mounted within the other. The collision of particles with the device results in a short circuit between adjacent metallic layers, which in turn provides an indication of the mass of the debris particle which impacted the device.
U.S. Pat. No. 3,004,735 discloses an inflatable panel adapted to be towed behind a launch vehicle to determine the debris particle environment in the vicinity of the vehicle. The energy content and frequency of particles colliding with the panel can be measured.
While the above patents recognize the significant adverse effects of debris colliding with active spacecraft, they do not teach an effective solution for reducing the population of threatening debris objects. Furthermore, these devices require complex maneuvering and excessive use of propellant for their maneuvering thrusters.
U.S. Pat. App. Pub. No. 2016/0023783 describes a spacecraft control unit configured to guide and navigate an apparatus to a target. The apparatus includes a dynamic object characterization unit configured to characterize movement, and a capture feature, of the target. The apparatus further includes a capture and release unit configured to capture a target and deorbit or release the target. A collection of these apparatuses is employed as multiple, independent and individually operated vehicles launched from a single launch vehicle for the purpose of disposing of multiple debris objects. This patent application employs a very expensive set of spacecraft that must maneuver to the targets. Excessive propellant and maneuvering time are required for each target before capture.
U.S. Pat. App. Pub. No. 2012/0068018 describes fiber-based debris interceptors that are used to intercept and/or contain space debris. The debris interceptors may be made up of fibers that are formed in space from a material supply on a space vehicle. These interceptors may be separated from the space vehicle and used to passively drift in order to remove debris from an orbit or to otherwise prevent debris from entering an orbit to avoid damaging a satellite or other spacecraft traveling in that orbit. The debris interceptors are not retrieved, but may be deployed prior to later launches of valuable spacecraft in order to “cleanse” the intended orbits of debris. Debris objects may pass through the debris interceptor, but in so doing may lose energy so as to de-orbit. This patent application describes a device that is used to protect one satellite at a time.
In “Catchers' Mitt as an Alternative to Laser Space Debris Mitigation,” Phipps describes the placement of a single block of low density material in an elliptical, near-equatorial orbit that would sweep out debris in near-Earth space between about 400 km and about 1100 km altitude. Phipps does not, however, address the control of this block or the challenge of avoiding active satellites. Nor does Phipps provide servicing or operating details for the block.
In “Aerogels Materials as Space Debris Collectors,” Woignier discusses the use of very light weight materials for use in space debris impact pads. Woignier does not, however, discuss the vehicles on which such materials would be used.
Thus, previously proposed orbital debris removal approaches require the use of extremely expensive and complex space systems in order to accomplish the removal of single debris objects. The implied complexity and expense of such approaches have prohibited any actual debris removal missions.